A video disc which is recorded with a television signal comprising a composite video signal and an audio signal is recorded with a plurality of fields of the television signal in one track turn (description will hereinafter be given for a case where four fields are recorded), in order to realize a large recording capacity under limitations such as practical diameter and rotational speed of the disc and a relative linear velocity between a pickup and the disc for obtaining a satisfactory signal-to-noise ratio. When playing this video disc in a still picture reproduction mode, the same track turn is scanned repeatedly. For this reason, in the still picture reproduction mode, the audio signal in the reproduced television signal is generally muted and the sound is not generated, while information in the four fields of the composite video signal are reproduced repeatedly. However, in the case where the picture content of the video signal which is to be reproduced relates to a moving picture, the pictures of the four fields recorded in one track turn are mutually different, and the picture reproduced in the still picture reproduction mode will not appear still but will appear as if it is undergoing a reciprocating movement. Hence, the reciprocating movement in the picture reproduced in the still picture reproduction mode becomes large as the movement in the moving picture becomes fast, and there is a disadvantage in that the picture reproduced in the still picture reproduction mode does not appear still and is awkward.
On the other hand, it is possible to consider recording a video information content of the same field repeatedly for four fields in one track turn and obtain a still picture by repeatedly scanning this one track turn. In this case, only the video information content of the same field is reproduced repeatedly even when the same track turn is scanned repeatedly, and it is possible to obtain a perfectly still picture.
However, when the video information of a first field is recorded repeatedly for four fields in a first track turn, the video information of a fifth field is recorded repeatedly for four fields in a second track turn and the video information of the same field is thereafter recorded repeatedly in each track turn for every four fields, it is possible to obtain a perfectly still picture in the still picture reproduction mode but a movement in the reproduced picture is awkward in a normal reproduction mode because 3/4 of the video information is missing.
On the other hand, when the video information of a first field is recorded repeatedly for four fields in a first track turn, the video information of a second field is recorded repeatedly for four fields in a second track turn and the video information of each field is thereafter recorded repeatedly in each track turn, it is possible to obtain a perfectly still picture in the still picture reproduction mode but there is a disadvantage in that a slow motion picture is reproduced in the normal reproduction mode because the video information of each field is reproduced four times. Furthermore, there is a disadvantage in that the audio signal cannot be reproduced normally from the disc which is recorded with the video information so that the perfectly still picture can be obtained in the still picture reproduction mode.
Accordingly, a disc was proposed in a U.S. Pat. No. 4,490,752, a British patent No. 2,099,202 and a West German patent No. 3212134.2-09 in which the assignee or applicant is the same as the applicant of the present application. According to the proposed disc, a video signal of the same unit is recorded repeatedly for a plurality of fields in each track turn, and divided audio signal portions which are obtained by dividing the audio signal for every field of the video signal which is reproduced are recorded sequentially on the track of the video signal according to a scanning locus of a pickup reproducing element which undergoes at least one forced track shift in two revolutions of the disc in the normal reproduction mode. In the still picture reproduction mode, it is possible to obtain a perfectly still picture by reproducing repeatedly the video signal of the same unit in the same track turn, and in the normal reproduction mode, it is possible to satisfactorily obtain a normally reproduced picture and a normally reproduced audio signal by causing the forced track shift of the pickup reproducing element at predetermined positions on the disc.
Because the divided audio signal portions are sequentially recorded according to the scanning locus of the pickup reproducing element at the time of the normal reproduction mode, there are track turns having a discontinuous point (edit point) where the information content of the audio signal becomes discontinuous. In addition, when recording the video disc, the television signal is successively recorded on the track turns from the outer periphery to the inner periphery of the disc (or vice versa), and the recording is continuously carried out at a constant speed without interruption due to the construction of a cutting machine. Accordingly, when recording the video disc, the audio signal must be generated in a pre-edited state with a sequence with which the audio signal is to be recorded and in synchronism with the composite video signal. The scanning locus of the pickup reproducing element in the normal reproduction mode is different for the cases where (1) the source of the composite video signal is a movie film having 30 picture frames per second, (2) the source of the composite video signal is video tape recorder (VTR) for playing a pre-recorded magnetic tape or a television camera and generates a video signal having 30 frames per second, and (3) the source of the composite video signal is a movie film having 24 picture frames per second. For this reason, the unit with which the audio signal is to be divided and the sequence of the divided audio signal portions must be selected depending on the source of the composite video signal.